Hao Huang

Originating from Hunan Province, China, Huangjin green tea (HJGT) is known for its diverse aromas, including green, floral, and chestnut-like, but their characteristic volatile components remain unclear. In this study, 111 volatiles were identified from 26 HJGT samples using HS-SPME-GC-MS. Floral HJGT showed the highest relative content of ester, chestnut-like HJGT was richest in sulfur-containing compounds, and green HJGT was dominated by alcohols. Partial least-squares discriminant analysis identified 61 differential volatiles (VIP > 1), whose distribution patterns across aroma types fell into four categories. Based on relative odor activity value (≥1) and ANOVA (p < 0.05), 26 key aroma-active compounds were further screened. Ten characteristic compounds, such as linalool, indole, and dimethyl sulfide contributed floral, fresh, green, cabbage, and violet-like notes to floral HJGT. Seven compounds, including heptanal, nonanal, and 2-pentylfuran, imparted nutty, waxy, pungent, and beany notes to chestnut-like HJGT. Nine compounds, including geraniol, hexanal, and phenylethyl alcohol, contributed green, floral, fragrant, and minty notes to green HJGT. These findings elucidate the chemical basis of HJGT aroma and provide a theoretical foundation for the targeted regulation of its aroma types in production.

Pile fermentation is a crucial process for developing the characteristic mellow taste and aged aroma of dark tea, yet the internal quality transformation mechanism of this process is still unclear. This study employed a high-sensitivity analytical platform based on gas chromatography–mass spectrometry (GC-MS) to systematically investigate the dynamic interplay between key chemical components, enzyme activities, and volatile compounds during the pile fermentation of primary dark tea. Our findings revealed a significant decrease in ester-type catechins, crude protein, and protopectin, alongside a notable accumulation of non-ester-type catechins, gallic acid, and soluble components. The multi-enzyme system—comprising PPO/POD, pectinase/cellulase, and protease—cooperatively drove the oxidation of phenols, cell wall degradation, and the release of aromatic precursors. This was complemented by GC-MS analysis, which identified and quantified 103 volatile compounds across nine chemical classes. The total content of volatile compounds increased significantly, with alcohols, esters, and aldehydes/ketones being the dominant groups. Floral and fruity compounds such as linalool and geraniol accumulated continuously, while esters exhibited an initial increase followed by a decrease. Notably, carotenoid degradation products, including β-ionone, were significantly enriched during the later stages. This study revealed a “oxidation–hydrolysis–reconstruction” metabolic mechanism co-driven by microbial activity and a multi-enzyme system, providing a theoretical foundation for the precise regulation of pile fermentation and targeted quality improvement of primary dark tea.

This study investigated the impact of storage temperatures (−20 °C, room temperature, and 40 °C) on the sensory evaluation, metabolites, and volatile compounds of green tea stored for 12 months. The sensory evaluation revealed that tea samples stored at −20 °C retained their emerald green colour, tender aroma, and refreshing taste. Green tea biochemical constituents, including water extracts and total free amino acids, were measured by Chinese National Standard Methods (GB/T 8305-2013 and GB/T 8314-2013). Tea polyphenols and flavonoids were determined using spectrophotometric methods, while phytochemicals were detected using validated HPLC, and volatile compounds were detected using validated gas chromatography coupled with triple quadrupole mass spectrometry. The analysis showed that tea polyphenols were highest at −20 °C, and flavonoids were significantly reduced at higher temperatures. A similar trend was observed for amino acids, soluble sugar content, and water extracts. Tea catechins, including (-)-epigallocatechin-3-gallate (EGCG) and (-)-gallocatechin gallate (GCG), were highest at −20 °C, showing their susceptibility to temperature. A volatile compound analysis revealed distinct profiles with variations in the abundance of compounds, such as di-methyl sulfide, phenyl ethyl alcohol, indole, and benzaldehyde. This study identifies temperature-sensitive compounds, providing insights into the mechanisms underlying tea quality deterioration during storage.

Tea aroma greatly varies with the production date. This study investigated the aroma differences among black teas processed on different dates (March 23rd, April 8th, April 15th, April 27th, and May 7th) in the spring. A sensory evaluation showed that the black tea produced on April 15th had a strong and lasting sweet aroma and the highest score of 93.5. In total, 71 volatile compounds were identified, and alcohols were the predominant category, accounting for 60.98%. From March 23rd to May 7th, the total content of volatile compounds showed a parabolic change trend and reached its maximum on April 15th (715.27 μg/L); the flavor index first peaked on April 8th (23.25) and then gradually decreased. A multivariate statistical analysis showed that 39 volatile compounds were important, differential aroma components. An odor activity value (OAV) analysis showed that the predominant odorants were β-ionone, β-damascenone, linalool, (E)-β-ocimene, and geraniol, all with values larger than 100. The total OAVs of undesirable odorants decreased and reached their minimum (70.4) on April 27th, while the total OAVs of pleasant odorants and the ratio of pleasant/undesirable odorants showed inverse changes and reached their maximum (2182.1 and 31.0, respectively) on April 27th. Based on the significance of differences and OAVs, linalool, (E)-β-ocimene, geraniol, and (E,E)-2,4-nonadienal were considered as the key differential odorants. Combined with the sensory evaluation and the differences in aroma components, it was proposed that black teas produced around April 15th in the Hunan district are more likely to have a strong and lasting sweet aroma. This study will provide scientific guidance for the production of black tea in the Hunan district, China.

Huangjin green tea (HJC) is one of the most famous regional green teas in China, and has gained attention for its unique flavor. Research on HJC has focused mainly on the synthesis of L-theanine, with fewer studies concentrating on sensory characteristics. In this study, molecular sensory science techniques, including color analysis, gas chromatography–ion mobility spectrometry, and E-tongue, were used to characterize the sensory properties of HJC, with Fuding Dabai and Anji Baicha teas used as conventional and high amino acid controls, respectively. The sensory characteristics and main quality components of HJC lie somewhere between these two other teas, and somewhat closer to the conventional control. They were difficult to distinguish by color, but significant differences exist in terms of volatile organic compounds (VOCs), E-tongue values on bitterness and astringency, and their contents of major taste components. VOCs such as (E)-2-octenal, linalool, ethyl acrylate, ethyl acetate, and 2-methyl-3-furanethiol were found to be the main differential components that contributed to aroma, significantly influencing the tender chestnut aroma of HJC. Free amino acids, tea polyphenols, and ester catechins were the main differential components responsible for taste, and its harmonious phenol-to-ammonia ratio was found to affect the fresh, mellow, heavy, and brisk taste of HJC.

Amino acids are the most important components of black tea and are associated with the physiological and biochemical changes that occur during tea processing. Herein, we review the enzymatic and non-enzymatic reactions of the main proteinaceous and non-proteinaceous amino acids that occur during the manufacturing process of black tea from the postharvest processing steps of tea leaves to the final product. Enzymatic reactions are responsible for the amino acid variation in the withering, rolling, and fermentation stages. The significant increase in the total amino acid content during the withering stage is mainly derived from proteolysis. Furthermore, the transformation reactions in the rolling and fermentation stages decrease the amino acid levels slightly, whereas the non-enzymatic reactions, such as the Maillard and Strecker reactions, contribute to the significant decrease in the amino acid content of the drying stage. This study provides deep insights into the mechanisms underlying amino acid variation during black tea processing.

The quality of Congou black tea fluctuates greatly with the changing seasons. However, variations in the taste quality of Congou black tea manufactured during a single spring season are far from clear. Here, we analyzed the taste quality of HuangJinCha (HJC) Congou black tea using sensory evaluation and found the taste quality of black tea manufactured in the early spring was better than that manufactured in the late spring. Principal component analysis (PCA) and cluster analysis for the data from the electronic tongue confirmed the variation and revealed that April 4 may be the critical time point at which variations in taste quality become apparent. The contents of tea polyphenols (TP), total catechins (TC), total flavones, (‐)‐epigallocatechin gallate (EGCG), (‐)‐epicatechin gallate (ECG), and gallic acid (GA) showed increasing trends, whereas total amino acids (TAA) declined over time. Moreover, the variations in total amino acids (r = 0.846) and total flavones (r = ‐ 0.858) were highly significantly correlated with the average taste quality score (p < .01), suggesting these compounds were the primary factors responsible for the fluctuation in taste quality of Congou black tea processed during a single spring season.